


Guy's Night

by SprucePines



Category: Gravity Falls
Genre: Accidental Voyeurism, Incest, M/M, Sibling Incest, Twincest
Language: English
Status: Completed
Published: 2015-03-11
Updated: 2015-03-11
Packaged: 2018-03-17 09:54:19
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,813
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/3524846
Author URL: https://archiveofourown.org/users/SprucePines/pseuds/SprucePines
Summary: <blockquote class="userstuff">
              <p>Double Dippin' AU. Mabel backs out of an evening with her friends in favor of spending it with her brothers. She decides to surprise them, but she ends up being the one surprised.</p>
            </blockquote>





	Guy's Night

**Author's Note:**

> Followers of pineneedleshurt on Tumblr may notice similarities between this story and her story "Why Not?" (http://pineneedleshurt.tumblr.com/post/66668240230/why-not). This wasn't intended when I started writing this, but became apparent to me about halfway through. Before I posted this on my own Tumblr, I sought her permission, which she graciously gave.

"Come on, Mabel," Hannah said, whining slightly. "You said you were gonna hang out with us tonight."

"I knooooow," Mabel said, "but Wednesday nights are 'Triplet Nights' for us."

"I thought you said your brothers were cool with it for tonight."

"That's what they said, but it's a tradition. I feel really bad for bailing on them."

"You mean like you're bailing on us?" Hannah said under her breath.

"Did you say something?" Mabel asked.

Hannah huffed. "I'm sorry Mabel-ine, but you and your brothers are weird."

"The weirdest!" Mabel affirmed. "This weekend for sure, I promise."As Hannah and the rest of her friends pulled away, she waved goodbye before turning towards the house. _Ha! Won't the guys be happy to see I decided to stay?_

Suddenly, an idea popped into her head. Dipper and Tyrone were out renting a movie for the evening. She could hide in their closet until they got back and jump out at them! Her smile grew wider as she bounded through the front door and up the stairs.

Carefully slipping into the boys' room, Mabel tiptoed over and around the minefield of discarded clothes and textbooks until she reached the closet. She stepped inside and closed the door, leaving herself a small crack to see through. From her current position she could see the door clearly. _Now we play the waiting game._

As she waited, she played out various scenarios in her head to see what the best option was. Option A was to spring out the moment Dip and Ty came in. They'd certainly be surprised, but they wouldn't have had a chance to settle back. Option B was to wait until just before they left their room to go watch whatever movie they chose. Again, no; they'd be mentally preparing for the movie. That left Option C, wait until the two were nice and settled before leaping out at them. Maximum surprise, possibly some frightened screams from Dipper, and then relief that it's only Mabel deciding to hang with her two favorite dorks instead of hanging at the mall with her friends.

Just as she had reached her decision, she heard the front door open, then close. From the entryway, she heard her brothers' muffled voices drift upstairs. As she heard the voices become more distinct, she knew they were coming to their room and peeked through the crack.

The door to the room swung open and Dipper came in first, wearing his ever-present red flannel and a blue stocking cap over his birthmark. Judging from the look on his face, he was fighting back laughter. Tyrone was right behind him, wearing a pullover sweater. He looked like he was struggling to breathe.

"And then," Tyrone gasped, "and then the guy says, 'Lady, I don't think I can _take_ sixty-seven more of _those_!'"

Both boys erupted into gales of laughter. Mabel hunched down, waiting for her just the right moment.

As their laughter subsided, Dipper's face grew a bit wistful. "Too bad Mabel decided to spend the evening with her friends," he said.

Tyrone sighed. "Yeah, I hear ya. But hey, that just means it's guy's night." He took a step towards his brother and placed a hand on Dipper's shoulder. "And you know what that means."

Mabel arched her eyebrow. _Guy's night? I wonder what that means. And what's with the way they're looking into each other's eyes? And--wait. Why are they leaning in...No...They're not..._

Mabel's eyes widened as she saw Tyrone's lips envelope Dipper's. This was not what she was expecting. Her brothers were kissing. Each other. And from the look of it, this was far from a new thing for them. Suddenly, this wasn't such a good idea. She had no idea how they'd react if she announced her presence now. But what could she do? Maybe there was a spell or something in the journal so she could melt through the closet wall and into her own room, but the journal was on Dipper's bookshelf.

So she was stuck here, at least until they finished making out and left the room. _OK. Just a little make out session between my brothers. Nothing to get all cray-cray about, Mabel girl. Just reach up and quietly close the door._

She reached for the knob. _That's it, now just pull it shut. Don't notice how Tyrone is grabbing Dipper's--Whoa now!_ She stared as Tyrone began squeezing Dipper's butt. Dipper grunted and moaned into his brother's mouth.

 _Come on, Mabelton!_ she admonished herself. _Just shut the door and ignore how...freaking hot it looks. These are your brothers, not a couple of guys doing a webcam video for the internet. Don't watch Dip pull at Tyrone's sweater. Don't you start salivating at Tyrone's body! Mabel? Mabel, no, I forbid you to get turned on by this!_

But her body had stopped listening to her brain long ago. Her hand fell away from the knob as Dipper was likewise stripped of his top. Dipper's hands reached up to Tyrone's face and gently pulled away. They were looking into each other's eyes again. And the grins on their faces... _Oh, what now?_

Dipper walked backwards towards his bed. Despite herself, Mabel shifted her position so she could continue watching them. As Dipper's legs reached the bed he fell backwards, bringing his brother down with him. Ty's hands slid up Dipper's torso, drawing out hums of pleasure. Tyrone began kissing his brother's chest, inching lower and lower.

_Oh, get out of town! He couldn't possibly..._

As Ty reached Dipper's pants, Mabel held her breath. _Is he really going to...?_ With a deliberate pace, Tyrone slowly pulled down the zipper of his brother's pants. The sound was like a jackhammer, driving the image even further into Mabel's mind. When she saw Tyrone pull Dip's pants down and their brother's penis sprang out, she had to cover her mouth to suppress a gasp.

"Did you hear something?" Dipper asked. Mabel froze. The silence in the closet was deafening.

"Yeah," Tyrone said. "The sweet sounds you make when I do this." And with that, he opened his mouth and engulfed Dipper's erection. Dipper groaned and Mabel marveled at the sight before her.

Now that the shock had begun to wear off, she was starting to find it...not as extreme as she initially thought. In fact, the more she considered it, the more she thought it was...appropriate. And along with that came a new sensation: desire. Watching her brothers engage in such an intimate act was making her question her own level of intimacy with the boys. Were they gay? Bi? Is this just a phase? And could there possibly be a place for her?

Mabel's breathing started getting heavy as she watched Tyrone blow Dipper. As Tyrone's head bobbed up and down, she found herself imagining being in Tyrone's place, servicing either or both of her brothers. She started to feel an itching between her thighs. _Ah, the heck with it._ Keeping her eyes locked on the display before her, she reached under her skirt and began to rub herself through her panties.

Ty continued to give his brother's penis a thorough wash. Occasionally, Dip would arch his back slightly and let out a tiny gasp. After a slightly louder one filled the room, Tyrone pulled off and gazed up at his brother.

"Wow, even your sexy gasps are cute."

Dipper glared down at him for a moment before breaking into a grin. He crooked his finger. "Bring yourself around up here. I'll show you who makes cute, sexy gasps." Tyrone stood and, with a grin, undid his pants, letting them drop to the floor. Stepping out of them, he climbed on the bed and positioned himself so they... _Hoo boy!_ Mabel's hand made its way inside her panties now.

Just when she thought it couldn't get any sexier, her brothers were now in a 69. As she watched the boys suck each other, her fingers made their way inside her folds. She imagined her fingers was actually one of her brother's cocks, penetrating deep inside her. She bit her lip, hoping that the noises the boys are making were masking her own.

Dipper reached for his bedside table, pulling open the drawer. From it, he pulled out a little bottle. It wasn't until she saw him squeeze a clear, slightly viscous liquid into his hand that she realized it was lube. Mabel gazed in awe as Dipper began working a couple of fingers into Tyrone's ass. Lube in one's butthole could only mean one thing. Her heart began to pound.

After a minute of loosening up, Ty released Dip from his mouth and spun himself around until he was straddling his brother. Dipper held his erection upright as Tyrone slowly lowered himself onto it. As she watched Dipper penetrate Tyrone, she pushed her fingers deeper inside of her, wishing she was in Tyrone's place.

Once Tyrone's butt reached Dipper's pelvis, he began bucking himself, riding Dipper. Their room was quickly filled with moans and groans. From her hiding place, Mabel was working herself over frantically. This was both the most outrageous and the most erotic thing she had ever seen in her life.

As he neared climax, Dipper began to thrust upward, trying to push his cock further into his brother. Tyrone met his brother's thrusts with each downward motion, trying to fill himself more.

With a final thrust Dipper came inside his brother, his cock throbbing as it filled Tyrone. The twitching sent vibrations through Tyrone's prostate, sparking electric waves of pleasure and sending him over the edge. His cum spurted out onto Dipper's chest and stomach.

Seeing her brothers both cum was too much for Mabel to handle and she collapsed in paroxysms, screaming out involuntarily.

A few moments later, as she recovered her senses, she realized that she had given herself away. In the dead silence of the room, a bolt of fear shot through her. A second later, she heard the creak of the floorboards as someone crossed to the closet. When the door was pulled open, she sheepishly looked up to see Tyrone, still naked, looking down at her. She risked a glance behind him and saw Dipper still on the bed, but he had covered himself with the comforter.

"Mabel?" Tyrone asked. "I thought you were going out with friends."

Mabel laughed nervously. "Yeah, but I thought I might surprise you. I guess you guys surprised _me_."

Tyrone looked back at their brother. Dipper's face was a mix of both anger and fear. _I gotta say something._

"So," she said, "I guess this is what you call 'guys night?'" Deciding to come clean she held up her hand, wet from her self-ministrations. "It looks like a lot of fun. Any chance you might consider counting me in?"


End file.
